Magnesium base alloy



Patented Mar. 13, 1945 UNlTED STATES PATENT OFFICE MAGNESIUM BASE ALLOYJohn C. McDonald, Midland, Mich., assignor to The Dow Chemical Company,Midland, Mich" a corporation of Michigan No Drawhig.

Application September 30, 1942, Serial No. 460,277

3 Claims. (01. 75-168) The invention relates to magnesium base alloysand moreparticularly concerns an alloy of this nature having a highdegree of formability associated with other desirable physicalproperties, such as good tensile strength, yield strength, and improvedcold rollability.

' Magnesium base alloys are being widely used in the structural artswhere a light weight metal is .highly desirable, such as for use inmaking castings, forgings, and the like. However, the use of thesealloys in the rolled form to make sheet metal articles requiring formingoperations, such as bending, drawing. and the like, has not progres'sedas rapidly due to the fact that, in general.

alloys having good formability or ductility permitting relatively sharpbends to be made without the article developing external cracks, usuallyhave inferior characteristics as regards their tensile and yieldstrengths.

strengths are manifest, over the entire range of composition indicated,I have found that in general alloys containing from about 0.5 to 3percent of thorium are endowed with the most satisfactory strength andformability characteristics,

on the other hand, the presence of from about Table 1 Annealed Coldrolled Nominal composition in per cent (magnasium-re- Per cent YieldTensile Yield Tensile mainder) elongastren h strength strength strengthTh tion in 2 in lbs sq. in lbs./ sq. in lbs./sq. in lbs/sq inches in.in. in.

It is, accordingly, the principal object of the invention to provide amagnesium base alloy which can be made into rolled sheet, and the like,

possessing a sufllcient degree of ductility or formability at ordinarytemperatures to be sharply bent, drawn, or otherwise shaped while havinggood tensile and yield strengths.

Another object of the invention is to provide a magnesium base alloypossessing improved cold rollability. 4

Other objects and advantages will be apparent as the description of theinvention proceeds.

My invention resides in the discovery that a magnesium base alloycomposed of from about 0.1 to 10.0 per cent of thorium, the balancebeing magnesium, possesses the aforementioned properties. The termmagnesium" used herein and in the appended claims is intended to includemagnesium containing the ordinary impurities that are found in thecommercially pure metal, such'as tracesof iron, copper, nickel, andsilicon. While the property of high tensile and yield The magnesium usedin preparing these alloys and for purposes of comparison was obtained by'subliming commercial magnesium.

The properties set forth in Table 1 under the term fannealed wereobtained by first rolling the alloys at a temperature of between 450 and700 and thereafter annealing them at various temperatures through arange of from 400 to 800 F. The properties selected for the tables werethose of the annealed specimens which exhibited the maximum elongation.The properties set forth under the term "cold rolled" were obtained bysubjecting specimens of the alloys which had first been hot rolled at atemperature of between 450 and 700 F. to additional rolling in the coldstate. The properties selected for the tables were those of the coldrolled specimens which showed the greatest tensile and yield strengths,while having at least a 1 per cent elongation in 2 inches.

A comparison of the properties listed in Table 1 shows that all of theproperties of my new amounts of thorium, in comparison to commercialmagnesium, is shown.

Table 2 Per cent reduction before edge cracking of first,

Nominal composition in percent second, and third de- (magnesium=remsinder) grees First Second Third Table 2 indicates the improvementof cold rollability of a binary magnesium-thorium alloy over commercialmagnesium when a sheet having a .070 gauge was rolled in an 8" mill at areduction per pass. In the table, the amount of edge cracking of therolled sheet is indicated by first; second, and third degrees. The firstdegree of edge cracking is defined as the point where very slight cracksappear at the edge of the rolled article, the second degree as the pointwhere a moderate number of cracks appear at the edge of the rolledarticle, and the third degree as the point where severe edge crackingoccurs, so severe as to cause the sheet to almost completely breakapart.

It will be noted from an examination of Table 2, that in the extremelylow percentage range of thorium addition, i. 9., 0.24 per cent, the coldrollability of the new alloy shows outstanding improvement over that ofcommercial magnesium.

While the new alloy is most useful in wrought form, such as sheets, dueto its formability characteristics, it may also be used for makingcastings, extruded forms, and the like. It is further pointed out thatmy new alloy is amenable to solution and precipitation heat treatments,which accordingly modify its properties.

The new alloy may be compounded by any of the methods usually employedfor melting and alloying metals with magnesium, such as by adding thethorium to a bath of molten magnesium, which is preferably protectedfrom oxidation by a suitable flux. It is sometimes desirable to add morethan the theoretical amount of thorium, since the alloying efficiency isnot always per cent and some loss may be incurred.

This application is a continuation-in-part of my co-pending applicationSerial No. 426,707, filed January 14, 1942; which, in turn, is acontinuation-impart of my application Serial No. 340,789, filed June 15,1940.

I claim:

1. A magnesium base alloy containing from 0.1 to 10 per cent of thorium,the balance being magnesium.

, 2. A magnesium basealloy containing from 0.5 to 3 per cent of thorium,the balance being magnesium.

3. A magnesium base alloy containing from 0.15 to 0.3 per cent ofthorium, the balance being magnesium.

JOHN C. MCDONALD.

